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The molecular structure of polyvinyl alcohol films and the effects of various modifiers on it
THE MOLECULAR STRUCTURE OF POLYVINYL ALCOHOL FILMS AND THE EFFECTS OF VARIOUS MODIFIERS ON IT* L. L. RAZUMOVA, h_. L. IORDA:gSKII, L. I . BULATIWIKOVA, O. V. SHATALOVA, I. G. TVERDO:gnT,EB, YU. V. lV[OISEYEV a n d G. YE. ZATgOV Chemical Physic Iustituto, U.S.S.R. Academy of Sciences
(Received 1 July 1975) Specific polymer properties as a function of structure b y the X-ray diffraction method are studied using polyvinyl alcohol (PVAlc) films produced by various mevh0ds and ~reatmen~s, as well as swelling in water. Depending on the preparation conditions, the PVAlc films have been found to possess either a sort of a laminar or steric structure. The swelling capacity of the films, or the amorphization of the structure when the PVAlc was dehydrated, correlated well with the ratio of the two structural types present in the PVAlc.
C~Az~G~,S in structure We are trying here to of PVAlc films, their of these films, namely
take place in polymers at various stages of preparation. trace the connection between the method of preparation molecular structure and one of the important properties the swelling capacity in water. EXPERIMENTAL
The samples used in this study differed in the method of preparation storage time, content of low mol. wt. additives, such as oxalic acid (OA) a n d p-toluonesulphonic acid (TSA). The PVAlc samples used were of type PVS-5 (Erevan plant "Polivinilatsetat") a n d had the following characteristics: mol. wt. = 65,000-68,000, 1.7 % acetate groups, 2.5% volatiles, acid n u m b e r 0.5 mg/g KOH, hot water (95°C) solubility=99.5%, ash content 1.43%. The methods of production of the films have been described before [1, 2]. X-ray diffraction was used in the structural study using a Cu filter a n d a sharply focusing X-ray source for photographic recording. The dehydrated samples were X-rayed either in special cassettes made of a non-swelling film having a diffraction picture defforont from t h a t of PVAle, or without cassettes, using a n electron-optical i n s t r u m e n t to make visible a n d to accelerate the recording (RSEOP) [3]. Using R S E O P along with wide anglo X-ray produced satisfactory records in 0.5-1 min; the study of thoprogross of swelling was made on a dry PVAlc film which was fixed in the clamps of the X-ray chamber; the start of the first X-ray photo coincided with placing a drop of water on both sides of the film, which immediately ran off; the periods elapsing between the X-ray records of PVAlc swelling wore based ou preliminary tests. Some films were subjected to normal photography of small angle X-rays pictures. I n order to determine the ratio of the irLtensities of rofloxions at 3.9 a n d 4-5 A (I3.9/I4.5) and also of the 5.5 and 4.5 reflexions (In.JI4.5), the X-ray pictures were photometored; the background scatter was calculated on photomicrographs by a graphical * Vysokomol. soyod. A18: No. 8, 1739-1743, 1976. 1989
1990
L. L. RAZU~OVA et al.
m e t h o d a n d t h e 3.9, 4.5 a n d 5.5 /~ reflexions w e r e isolated. T h e reflexion c o n t o u r s w e r e transferred on to a tracing paper, then cut out and the intensity ratios evaluated gravi. m e t r i c a l l y . T h e a v e r a g e r e s u l t s of all of t h e r e s p e c t i v e X - r a y p i c t u r e s a t a n a v e r a g e d e t e r . r u i n a t i o n e r r o r of ± 0 . 0 5 , are g i v e n in T a b l e 2.
RESULTS
The PVAlc samples are known to have various crystalline to amorphous phase ratios [4]. An important feature of crystalline PVA]c is that the polymer chains are organized in a laminar structure [5] in which layers formed by van der Waals forces alternate with those due to hydrogen bonds [6-8]. The structural units of this laminar structure are chain pairs linked partly by H bonds as in dimers and formed, for example, as a result of the "fork-like" H bonds of any formic acid present [9]. The other part of the H bond binds these dimers together into the so-called binary layer. The parameters of this PVAlc elemental cell can vary within certain limits [4, 10]. Distler and Pinsker [ 11] discovered still another form of PVAlc, namely a pseudo-crystalline structure of the bundle type. TABLE 1.
THE
MAIN REFLEXION INTENSITIES IN THE X-RAY
P I C T U R E S OF V A R I O U S
PVAIe
FILMS
hkl
Lattice period,
A 100 001 101 200 002
7.8 5-5 4.5 3.9 2-8
Intensities calculated on a 100 scale for a [11] laminar cryst. structure
pseudo-cryst. (bundle) structure
__$
E x p . i n t e n s i t i e s on a scale u p to 5 f o r films o f t y p e laminar perfect imperfect structure structure
pseudocrystalline
3 1
100 56 11
100 0 0
5 4 1
* The results cited in [11] are not given.
Turning now to the X-ray study of PVAlc films, we considered the possibility of a complex structural composition present in the pictures, i.e. of the ref l e x i o n s of amorphous, crystalline, laminar, and of pseudo-crystalline phases. The X-ray picture of the amorphous phase has two typical diffuse reflexions present around 4-5 and 8-10 A; those of the bundle and laminar type of phases are listed in Table 1. The most characteristic feature of the laminar structure is the 3.9 A reflexions. All the dry PVAlc films examined contained the amorphous and crystalline or pseudo-crystalline phases (Fig. la-c).The films with the most perfect crystalline structure were produced from PVAlc solutions in a binary solvent (waterethanol) and by drying at 135°C. The respective X-ray pictures (Fig. la) contain all the intense reflexions expected of such a structure [5].
Molecular structure of polyvinyl alcohol films
1991~
T h e v e r y m u c h w e a k e r or diffuse 001 reflexions shown in Fig. lb were g o t f r o m PVAlc films p r o d u c e d f r o m aqueous solutions a n d dried a t 1350C. T h e reason could be a n insufficiently clear lateral packing of the dimers in t h e l a y e r s w i t h a crystalline structure.
a I~ .5
b
b-0
I
G' J0
i
d
\ /0 '
' ~
2 Fzo. 1
,'
I°1
u
G
n
n
I
10
,
,
,°1
nl
t
lq 2q 26 Time, rnin
Fxo. 2
FIG. 1. X-ray diffraction pictures (produced in a cylindrical camera) of PVAIc films: a --with a perfect crystal (laminar) structure [5]; b --with a laminar structure and imperfections in layer direction; c--with a pseudo-crystalline structure; d--with a laminar structure after dehydrating amorphization of she film. The arrows indicate the main X-ray reflexions. FIG. 2. The progress of molecular structure amorphization in some of the PVAle films as a function of swelling time in water (according to the RSEOP pictures, and the parameter of 4.5 ~ reflexion intensity decrease). Diffractogram lc was o b t a i n e d f r o m films p r o d u c e d f r o m aqueous PVAI~solutions k e p t a t 95°C a t t h e start, which were t h e n dried at r o o m t e m p e r a t u r e . This picture does n o t contain the reflexions typical for a l a m i n a r s t r u c t u r e [5], b u t is r e m i n i s c e n t of the pseudo-crystalline t y p e of PVAlc [11], T h e H b o n d s . o u g h t to be isotropic here w i t h respect to the m a i n chain direction a n d c r e a t e a steric n e t w o r k of bonds [12]. T h e PVAlc films p r o d u c e d b y various m e t h o d s t h u s show s t r u c t u r a l differences of t h e orderly a r r a n g e d phases. One could suggest some q u a n t i t a t i v e X - r a y features for the purpose of e v a l u a t i n g t h e s t r u c t u r e in such films, especially t h e p a r a m e t e r suggested as a f e a t u r e o f the " l a m i n a r " s t r u c t u r e in the case o f p o l y eaproamides [13]; the h y d r o g e n bonds again p l a y a n i m p o r t a n t p a r t in its structure. T h e r e l e v a n t indicator is the ratio o f t h e 3.9 a n d 4-5 A integral reflexion intensities. I n t h e case of P V A l c with a perfect laminar structure, this indicator-
L. L RAZUMOVAe~ al.
1992
should be about 0.6 [11]. All our samples were found to have a lower than the c~leulated ratio, as Table 2 shows. I3.,/I~. s ought to be zero for a pseudo-crystalline structure [11]. The films p r o d u c e d at lower than 95°C showed this value to be larger than zero (Table 2), which means that the laminar structure plays a ~mall part in that of such films. We suggest as the other indicator the ratio of integral reflexion intensities (I5.5/I4.5); it characterizes the degree of perfection of the layers existing in the polymer bulk, preferentially that of the dimer bonding into a binary layer. This particular indicator distinguishes between the PVAlc films produced at 135°C from binary solvent and aqueous solutions. TABLE
2.
LAMINARITY RANGED
XoRAY OF
PV~Llc
DIFFRACTION THE
MOLECULA~
FRACTION ERIC
PARAMETERS STRUCTURE
(I3.,/I~.5)
AND
CHAIN ORGANIZATION
PVAle film production method At 135°Cfrom a water/ethanol mixture At 135°Cfrom an aqueous solution At room temperature from an aqueous solution
CHARACTERIZII~G
TH.~
IN
AR-
THE
ORDERLY
Tli~: PERFECTION
OF
DI-
(I5.5/I4.5) I..8/I4.5 0.35 0.35 0-15
I5.5/I4.s 0.25 0.10 ~0
We are thus able to examine the fairly distinct dependence of the structure in the orientated phase on the method of PVAle film production. When the latter is carried out at elevated temperature (135°C) one finds a laminar molecular structure which is more perfect when the PVAlc is dissolved in a binary solvent when compared with that produced from an aqueous solution. A film produced a t room temperature has a near pseudo-crystalline structure of the orientated part. It seems that the higher temperature causes the H bonds to recombine in the polymer to dimers and the binary layers are the result. The addition of small modifier quantitaties, such as OA (1-3%) or TSA (3%), alters some of the PVAlc film properties; the diffusion characteristic is one such property [14]. According to the diffraction pictures from dry PVAle films, which possess a laminar crystalline structure, there is no difference between the samples receiving different modifiers and those without them. No significant changes were seen in the wide angle X-ray pictures after storage in air for a b o u t 3 years. The picture is quite different after the PVAle films have been wetted (see below). One of the properties we used was the swelling capacity of the PVAle films to various degrees in water. This property is normally associated with the ratio o f crystalline to amorphous phases present in the films [4]. Our findings show t h a t other structural characteristics of PVAlc, associated with the H bond distribution and the indicators from the X-ray pictures for the structure in the ordered phases, are more significant.
Molecular structure of polyvinyl alcohol films
1993
For example, the films with a laminar crystalline structure become completely amorphous as a result of swelling in water (Fig. ld); the X-ray picture taken of such a film does not contain any well defined reflexions which would indicate the retention of any part of the crystalline phase. Subsequent drying (also at room temperature) of the amorphized films restores the original laminar structure as evident in the X-ray pictures. The wetting of PVAlc films of laminar structure thus causes the separation of the molecular layers.
FIG. 3. The X-ray diffraction pie~uro of a dry PVAle film produced by using PSEOP after 30 sec; tho arrow indicates the 4.5/~ reflexion.
PVAlc films with a pseudo-crystalline structure hardly swell in water; there is no change in the X-ray picture after immersion of the films in water. The films with a laminar structure were not any more completely amorphous when wetted; after storage in air for 3 years this appears to be due to some transversal crosslinkages having formed in this time. Although no effect of modifiers and ageing shows up in the X-ray pictures of dry PVAlc films, it can be detected after swelling in water. There is good reason to believe that the distinct 4-5 A reflexion detected in the X-ray pictures of all the stored wet samples is due to an amorphization during wetting of that part of the structure in which there is a network of H bonds (the pseudo-crystalline fraction of PVAlc), or co-valent bonds (after ageing, in the films modified with OA); this network prevents the molecular layers or chains to come apart (to separate) when the film is immersed in water. We examined the progress of the structural changes during PVAlc film swelling b y recording the R S E O P at 30-60 sec exposures from the early stages of wetting onwards (Fig. 2, 3). The comparisons of consecutive pictures of samples with a laminar structure showed that the wetting did not create fresh crystal modifications, b u t that the crystalline part rapidly turned into an amorphous one. The diagram reproduced in Fig. 2 shows the structural changes in the films (a quantitative evaluation of the wetting process was carried out b y measuring the 4.5/~ reflexion intensity on the X-ray pictures after various periods of wet.-
1994
L. L. RAZUMOVA e~ al.
ring b y p h o t o m e t r y of separate frames of the R S E O P p h o t o g r a p h i c film and b y measuring the a m p l i t u d e of the 4.5 A peak a b o v e t h e base-line). One can see amorp h i z a t i o n of the r e l e v a n t p a r t to be v e r y rapid, i.e. in t h e first few minutes o f wetting. Some p a r t o f the s t r u c t u r e n o t a m o r p h i z e d during this period remains u n c h a n g e d for a long time. W e h a v e t h u s shown t h a t various PVAlc film p r e p a r a t i o n conditions will give samples with differing s t r u c t u r e o f t h e orderly a r r a n g e d phase a n d also swelling capacities. T h e least resistant to w a t e r p e n e t r a t i o n are t h e films w i t h a well developed laminar s t r u c t u r e w h e n p r o d u c e d u n d e r conditions ensuring a r e c o m b i n a t i o n possibility of t h e H bonds t o p r o d u c e t h e energetically more f a v o u r a b l e laminar structure. T h e a m o r p h i z a t i o n o f the l a t t e r b y wetting t a k e s place in a few minutes a n d is reversible. Translated
by K. A. Az.z~N
REFERENCES
1. L. I. BUI~TNIKOVA, O. N. BELYATSKAYA and V. Ye. GUL, Plast. Massy, No. 3, 8, 1969 2. L. I. BULATNIKOVA, Dissertation, 1972 3. V. A. VYZGUNOV, M. M. BUTSLOV and M. A. MOKUL'SKH~ I)okl. Akad. Nauk SSSI% 185: 782, 1969 4. S. N. USHAKOV, Polivinilovyi spirt i ego proizvodnye (Polyvinyl Alcohol and its Derivatives). Izd. Akad. Nauk SSSR, 269, 1960 5. G. W. BUNN, Nature 161: 929, 1948 6. S.N. ZHURKOV and B. I. LEVIN, Dokl. Akad. Nauk SSSR 67: 89, 1949 7. Ye. F. GROSS and Ya. I. RYSKIN, Sb.: K 70-1etiyu A. F. Ioffe (Coll.: To the 70th birthday of A. F. Ioffe). Izd. Akad. Nauk SSSR, 249, 1950 8. K. FUJII, T. MOCHIZUKI, S. IMOTO, J. U K m A and M. MATSUMOTO, J. Polymer Sci. A2: 2327, 1964 9. A. I. KITAIGORODSKII, Organicheskaya kristallokhimiya (Organic Crystal Chemistry). Izd. Akad. Nauk SSSR, 1955 10. T. MOCHIZUKI, J. Chem. Soc. Japan 81: 15, 1960 11. G. I. DISTLER and Z. G. PINSKER, Zhur. fiz. Khim. 24: 1152, 1950 12. V. A. KARGIN, I. V. PIS'MENKO and Ye. P. CHERNEVA, Vysokomol. soyed. A1O: 846, 1968 (Translated in Polymer Sei. U.S.S.R. 10: 4, 981, 1968) 13. A. N. MACHULIS and E. TORNAU, I)iffuzionnaya stabflizatsiya polhnerov (The Diffusion Stabilization of Polymers). Vilnyus, 81, 1974 14. A. L. IORDANSKII, L. I . RUI~TNIKOVA and O. N. BELYATSKAYA, Tezisy dokladov 3-i Vsesoyuz. Konf. po stareniyu i stabilizatsii polimerov (Reports from 3 rd AllUnion Conf. on Ageing and Stabilization of Polymers). Moscow, 163, 1971
(Received 1 July 1975) Specific polymer properties as a function of structure b y the X-ray diffraction method are studied using polyvinyl alcohol (PVAlc) films produced by various mevh0ds and ~reatmen~s, as well as swelling in water. Depending on the preparation conditions, the PVAlc films have been found to possess either a sort of a laminar or steric structure. The swelling capacity of the films, or the amorphization of the structure when the PVAlc was dehydrated, correlated well with the ratio of the two structural types present in the PVAlc.
C~Az~G~,S in structure We are trying here to of PVAlc films, their of these films, namely
take place in polymers at various stages of preparation. trace the connection between the method of preparation molecular structure and one of the important properties the swelling capacity in water. EXPERIMENTAL
The samples used in this study differed in the method of preparation storage time, content of low mol. wt. additives, such as oxalic acid (OA) a n d p-toluonesulphonic acid (TSA). The PVAlc samples used were of type PVS-5 (Erevan plant "Polivinilatsetat") a n d had the following characteristics: mol. wt. = 65,000-68,000, 1.7 % acetate groups, 2.5% volatiles, acid n u m b e r 0.5 mg/g KOH, hot water (95°C) solubility=99.5%, ash content 1.43%. The methods of production of the films have been described before [1, 2]. X-ray diffraction was used in the structural study using a Cu filter a n d a sharply focusing X-ray source for photographic recording. The dehydrated samples were X-rayed either in special cassettes made of a non-swelling film having a diffraction picture defforont from t h a t of PVAle, or without cassettes, using a n electron-optical i n s t r u m e n t to make visible a n d to accelerate the recording (RSEOP) [3]. Using R S E O P along with wide anglo X-ray produced satisfactory records in 0.5-1 min; the study of thoprogross of swelling was made on a dry PVAlc film which was fixed in the clamps of the X-ray chamber; the start of the first X-ray photo coincided with placing a drop of water on both sides of the film, which immediately ran off; the periods elapsing between the X-ray records of PVAlc swelling wore based ou preliminary tests. Some films were subjected to normal photography of small angle X-rays pictures. I n order to determine the ratio of the irLtensities of rofloxions at 3.9 a n d 4-5 A (I3.9/I4.5) and also of the 5.5 and 4.5 reflexions (In.JI4.5), the X-ray pictures were photometored; the background scatter was calculated on photomicrographs by a graphical * Vysokomol. soyod. A18: No. 8, 1739-1743, 1976. 1989
1990
L. L. RAZU~OVA et al.
m e t h o d a n d t h e 3.9, 4.5 a n d 5.5 /~ reflexions w e r e isolated. T h e reflexion c o n t o u r s w e r e transferred on to a tracing paper, then cut out and the intensity ratios evaluated gravi. m e t r i c a l l y . T h e a v e r a g e r e s u l t s of all of t h e r e s p e c t i v e X - r a y p i c t u r e s a t a n a v e r a g e d e t e r . r u i n a t i o n e r r o r of ± 0 . 0 5 , are g i v e n in T a b l e 2.
RESULTS
The PVAlc samples are known to have various crystalline to amorphous phase ratios [4]. An important feature of crystalline PVA]c is that the polymer chains are organized in a laminar structure [5] in which layers formed by van der Waals forces alternate with those due to hydrogen bonds [6-8]. The structural units of this laminar structure are chain pairs linked partly by H bonds as in dimers and formed, for example, as a result of the "fork-like" H bonds of any formic acid present [9]. The other part of the H bond binds these dimers together into the so-called binary layer. The parameters of this PVAlc elemental cell can vary within certain limits [4, 10]. Distler and Pinsker [ 11] discovered still another form of PVAlc, namely a pseudo-crystalline structure of the bundle type. TABLE 1.
THE
MAIN REFLEXION INTENSITIES IN THE X-RAY
P I C T U R E S OF V A R I O U S
PVAIe
FILMS
hkl
Lattice period,
A 100 001 101 200 002
7.8 5-5 4.5 3.9 2-8
Intensities calculated on a 100 scale for a [11] laminar cryst. structure
pseudo-cryst. (bundle) structure
__$
E x p . i n t e n s i t i e s on a scale u p to 5 f o r films o f t y p e laminar perfect imperfect structure structure
pseudocrystalline
3 1
100 56 11
100 0 0
5 4 1
* The results cited in [11] are not given.
Turning now to the X-ray study of PVAlc films, we considered the possibility of a complex structural composition present in the pictures, i.e. of the ref l e x i o n s of amorphous, crystalline, laminar, and of pseudo-crystalline phases. The X-ray picture of the amorphous phase has two typical diffuse reflexions present around 4-5 and 8-10 A; those of the bundle and laminar type of phases are listed in Table 1. The most characteristic feature of the laminar structure is the 3.9 A reflexions. All the dry PVAlc films examined contained the amorphous and crystalline or pseudo-crystalline phases (Fig. la-c).The films with the most perfect crystalline structure were produced from PVAlc solutions in a binary solvent (waterethanol) and by drying at 135°C. The respective X-ray pictures (Fig. la) contain all the intense reflexions expected of such a structure [5].
Molecular structure of polyvinyl alcohol films
1991~
T h e v e r y m u c h w e a k e r or diffuse 001 reflexions shown in Fig. lb were g o t f r o m PVAlc films p r o d u c e d f r o m aqueous solutions a n d dried a t 1350C. T h e reason could be a n insufficiently clear lateral packing of the dimers in t h e l a y e r s w i t h a crystalline structure.
a I~ .5
b
b-0
I
G' J0
i
d
\ /0 '
' ~
2 Fzo. 1
,'
I°1
u
G
n
n
I
10
,
,
,°1
nl
t
lq 2q 26 Time, rnin
Fxo. 2
FIG. 1. X-ray diffraction pictures (produced in a cylindrical camera) of PVAIc films: a --with a perfect crystal (laminar) structure [5]; b --with a laminar structure and imperfections in layer direction; c--with a pseudo-crystalline structure; d--with a laminar structure after dehydrating amorphization of she film. The arrows indicate the main X-ray reflexions. FIG. 2. The progress of molecular structure amorphization in some of the PVAle films as a function of swelling time in water (according to the RSEOP pictures, and the parameter of 4.5 ~ reflexion intensity decrease). Diffractogram lc was o b t a i n e d f r o m films p r o d u c e d f r o m aqueous PVAI~solutions k e p t a t 95°C a t t h e start, which were t h e n dried at r o o m t e m p e r a t u r e . This picture does n o t contain the reflexions typical for a l a m i n a r s t r u c t u r e [5], b u t is r e m i n i s c e n t of the pseudo-crystalline t y p e of PVAlc [11], T h e H b o n d s . o u g h t to be isotropic here w i t h respect to the m a i n chain direction a n d c r e a t e a steric n e t w o r k of bonds [12]. T h e PVAlc films p r o d u c e d b y various m e t h o d s t h u s show s t r u c t u r a l differences of t h e orderly a r r a n g e d phases. One could suggest some q u a n t i t a t i v e X - r a y features for the purpose of e v a l u a t i n g t h e s t r u c t u r e in such films, especially t h e p a r a m e t e r suggested as a f e a t u r e o f the " l a m i n a r " s t r u c t u r e in the case o f p o l y eaproamides [13]; the h y d r o g e n bonds again p l a y a n i m p o r t a n t p a r t in its structure. T h e r e l e v a n t indicator is the ratio o f t h e 3.9 a n d 4-5 A integral reflexion intensities. I n t h e case of P V A l c with a perfect laminar structure, this indicator-
L. L RAZUMOVAe~ al.
1992
should be about 0.6 [11]. All our samples were found to have a lower than the c~leulated ratio, as Table 2 shows. I3.,/I~. s ought to be zero for a pseudo-crystalline structure [11]. The films p r o d u c e d at lower than 95°C showed this value to be larger than zero (Table 2), which means that the laminar structure plays a ~mall part in that of such films. We suggest as the other indicator the ratio of integral reflexion intensities (I5.5/I4.5); it characterizes the degree of perfection of the layers existing in the polymer bulk, preferentially that of the dimer bonding into a binary layer. This particular indicator distinguishes between the PVAlc films produced at 135°C from binary solvent and aqueous solutions. TABLE
2.
LAMINARITY RANGED
XoRAY OF
PV~Llc
DIFFRACTION THE
MOLECULA~
FRACTION ERIC
PARAMETERS STRUCTURE
(I3.,/I~.5)
AND
CHAIN ORGANIZATION
PVAle film production method At 135°Cfrom a water/ethanol mixture At 135°Cfrom an aqueous solution At room temperature from an aqueous solution
CHARACTERIZII~G
TH.~
IN
AR-
THE
ORDERLY
Tli~: PERFECTION
OF
DI-
(I5.5/I4.5) I..8/I4.5 0.35 0.35 0-15
I5.5/I4.s 0.25 0.10 ~0
We are thus able to examine the fairly distinct dependence of the structure in the orientated phase on the method of PVAle film production. When the latter is carried out at elevated temperature (135°C) one finds a laminar molecular structure which is more perfect when the PVAlc is dissolved in a binary solvent when compared with that produced from an aqueous solution. A film produced a t room temperature has a near pseudo-crystalline structure of the orientated part. It seems that the higher temperature causes the H bonds to recombine in the polymer to dimers and the binary layers are the result. The addition of small modifier quantitaties, such as OA (1-3%) or TSA (3%), alters some of the PVAlc film properties; the diffusion characteristic is one such property [14]. According to the diffraction pictures from dry PVAle films, which possess a laminar crystalline structure, there is no difference between the samples receiving different modifiers and those without them. No significant changes were seen in the wide angle X-ray pictures after storage in air for a b o u t 3 years. The picture is quite different after the PVAle films have been wetted (see below). One of the properties we used was the swelling capacity of the PVAle films to various degrees in water. This property is normally associated with the ratio o f crystalline to amorphous phases present in the films [4]. Our findings show t h a t other structural characteristics of PVAlc, associated with the H bond distribution and the indicators from the X-ray pictures for the structure in the ordered phases, are more significant.
Molecular structure of polyvinyl alcohol films
1993
For example, the films with a laminar crystalline structure become completely amorphous as a result of swelling in water (Fig. ld); the X-ray picture taken of such a film does not contain any well defined reflexions which would indicate the retention of any part of the crystalline phase. Subsequent drying (also at room temperature) of the amorphized films restores the original laminar structure as evident in the X-ray pictures. The wetting of PVAlc films of laminar structure thus causes the separation of the molecular layers.
FIG. 3. The X-ray diffraction pie~uro of a dry PVAle film produced by using PSEOP after 30 sec; tho arrow indicates the 4.5/~ reflexion.
PVAlc films with a pseudo-crystalline structure hardly swell in water; there is no change in the X-ray picture after immersion of the films in water. The films with a laminar structure were not any more completely amorphous when wetted; after storage in air for 3 years this appears to be due to some transversal crosslinkages having formed in this time. Although no effect of modifiers and ageing shows up in the X-ray pictures of dry PVAlc films, it can be detected after swelling in water. There is good reason to believe that the distinct 4-5 A reflexion detected in the X-ray pictures of all the stored wet samples is due to an amorphization during wetting of that part of the structure in which there is a network of H bonds (the pseudo-crystalline fraction of PVAlc), or co-valent bonds (after ageing, in the films modified with OA); this network prevents the molecular layers or chains to come apart (to separate) when the film is immersed in water. We examined the progress of the structural changes during PVAlc film swelling b y recording the R S E O P at 30-60 sec exposures from the early stages of wetting onwards (Fig. 2, 3). The comparisons of consecutive pictures of samples with a laminar structure showed that the wetting did not create fresh crystal modifications, b u t that the crystalline part rapidly turned into an amorphous one. The diagram reproduced in Fig. 2 shows the structural changes in the films (a quantitative evaluation of the wetting process was carried out b y measuring the 4.5/~ reflexion intensity on the X-ray pictures after various periods of wet.-
1994
L. L. RAZUMOVA e~ al.
ring b y p h o t o m e t r y of separate frames of the R S E O P p h o t o g r a p h i c film and b y measuring the a m p l i t u d e of the 4.5 A peak a b o v e t h e base-line). One can see amorp h i z a t i o n of the r e l e v a n t p a r t to be v e r y rapid, i.e. in t h e first few minutes o f wetting. Some p a r t o f the s t r u c t u r e n o t a m o r p h i z e d during this period remains u n c h a n g e d for a long time. W e h a v e t h u s shown t h a t various PVAlc film p r e p a r a t i o n conditions will give samples with differing s t r u c t u r e o f t h e orderly a r r a n g e d phase a n d also swelling capacities. T h e least resistant to w a t e r p e n e t r a t i o n are t h e films w i t h a well developed laminar s t r u c t u r e w h e n p r o d u c e d u n d e r conditions ensuring a r e c o m b i n a t i o n possibility of t h e H bonds t o p r o d u c e t h e energetically more f a v o u r a b l e laminar structure. T h e a m o r p h i z a t i o n o f the l a t t e r b y wetting t a k e s place in a few minutes a n d is reversible. Translated
by K. A. Az.z~N
REFERENCES
1. L. I. BUI~TNIKOVA, O. N. BELYATSKAYA and V. Ye. GUL, Plast. Massy, No. 3, 8, 1969 2. L. I. BULATNIKOVA, Dissertation, 1972 3. V. A. VYZGUNOV, M. M. BUTSLOV and M. A. MOKUL'SKH~ I)okl. Akad. Nauk SSSI% 185: 782, 1969 4. S. N. USHAKOV, Polivinilovyi spirt i ego proizvodnye (Polyvinyl Alcohol and its Derivatives). Izd. Akad. Nauk SSSR, 269, 1960 5. G. W. BUNN, Nature 161: 929, 1948 6. S.N. ZHURKOV and B. I. LEVIN, Dokl. Akad. Nauk SSSR 67: 89, 1949 7. Ye. F. GROSS and Ya. I. RYSKIN, Sb.: K 70-1etiyu A. F. Ioffe (Coll.: To the 70th birthday of A. F. Ioffe). Izd. Akad. Nauk SSSR, 249, 1950 8. K. FUJII, T. MOCHIZUKI, S. IMOTO, J. U K m A and M. MATSUMOTO, J. Polymer Sci. A2: 2327, 1964 9. A. I. KITAIGORODSKII, Organicheskaya kristallokhimiya (Organic Crystal Chemistry). Izd. Akad. Nauk SSSR, 1955 10. T. MOCHIZUKI, J. Chem. Soc. Japan 81: 15, 1960 11. G. I. DISTLER and Z. G. PINSKER, Zhur. fiz. Khim. 24: 1152, 1950 12. V. A. KARGIN, I. V. PIS'MENKO and Ye. P. CHERNEVA, Vysokomol. soyed. A1O: 846, 1968 (Translated in Polymer Sei. U.S.S.R. 10: 4, 981, 1968) 13. A. N. MACHULIS and E. TORNAU, I)iffuzionnaya stabflizatsiya polhnerov (The Diffusion Stabilization of Polymers). Vilnyus, 81, 1974 14. A. L. IORDANSKII, L. I . RUI~TNIKOVA and O. N. BELYATSKAYA, Tezisy dokladov 3-i Vsesoyuz. Konf. po stareniyu i stabilizatsii polimerov (Reports from 3 rd AllUnion Conf. on Ageing and Stabilization of Polymers). Moscow, 163, 1971